Shoes soles, in particular midsoles, play an important role in the construction of shoes. They protect the wearer's foot against injuries caused for example by sharp objects. In addition, a shoe sole may provide cushioning to cushion the forces which occur when the shoe contacts the ground. In order to provide such a plurality of functionalities, shoe soles, in particular shoe soles for sports shoes, are usually manufactured by molding and foaming polymers. Some examples of common foam materials for shoe soles are, ethylene-vinyl acetate (EVA), and thermoplastic polyurethane (TPU).
In recent times, the demand for improved performance properties in shoe soles has increased, in particular in shoe soles for sports shoes. The demand for increased performance has led to the need for improved materials, new materials and new processing methods to meet the performance requirements.
In one approach, individual expanded particles or the like are filled into a cavity and molded. For example, applicant disclosed in EP 2 786 670 A1 and EP 2 649 896 A1 methods for manufacturing cushioning elements as well as shoe soles comprising a plurality of expanded TPU particles.
However, a common disadvantage of these manufacturing methods is that they are very complicated and in particular not easily adapted to provide a shoe sole with a plurality of functionalities according to customers' needs and requirements. For example, in the shoe soles of the described applications, EP 2 786 670 A1 and EP 2 649 896 A1, the particles are fused at their outer surfaces through the application of heat. However, it is difficult to provide different cushioning properties in different parts of the shoe sole. It is possible that different cushioning properties could be provided by using particles having different base properties and composition, for example, through adjusting the base recipe via altering the chemical composition of the particles, for example, by altering the base polymer. However, the use of different particles may cause difficulties in the logistics of the supply chain, the storage of the particles, and/or delivery of the particles to the production steps at the correct time, quantity and location during the mass production of shoe soles.
Therefore, the underlying problem of the present invention is to provide an improved method for manufacturing at least a part of a molded sporting good, in particular a sole for a shoe from individual expanded particles, which is capable to at least partly overcome some of the above mentioned deficiencies of the prior art.